This invention relates to a method for preparing catalysts useful in the manufacture of dicarboxylic acid anhydrides by the oxidation of hydrocarbons. More particularly, it is directed to the preparation of high yield catalysts suitable for producing maleic anhydride from saturated hydrocarbons at lower temperatures than heretofore thought possible.
Maleic anhydride is used alone or in combination with other acids in the manufacture of alkyd and polyester resins. It is also a versatile intermediate for chemical synthesis. Significant quantities of maleic anhydride are produced each year to satisfy these needs.
U.S. Pat. No. 3,293,268 teaches a process of oxidizing saturated aliphatic hydrocarbons to maleic anhydride under controlled temperature conditions and in the presence of phosphorus-vanadium-oxygen catalysts. A method of preparing such catalysts involved reacting phosphoric acid with a vanadium compound in aqueous hydrochloric acid solution, recovering the remaining solids by evaporating the solution to dryness, and then heating the solids to 300.degree. to 500.degree. C. The resulting catalysts were ground to pass a 20 mesh screen and pelleted to form tablets.
Numerous methods have been devised for increasing the activity of the catalyst as by the inclusion of activating additives, controlled levels of heat application in the calcinating step and the like.
As would be expected, any method for the preparation of the phosphorus-vanadium-oxygen catalyst which increases its yield of maleic anhydride could be a significant advance in the art and is an object of this invention.